1. Field of the Invention
The present invention is generally related to broadband communication systems. More particularly, the present invention is related to broadband communications systems that use Data Over Cable Service Interface Specification (DOCSIS) or any of its derivatives, including but not limited to a DOCSIS-compliant two-way satellite communication system. In addition, the present application is not limited to systems which utilize DOCSIS and may easily be applied to other communication system specifications and protocols that use adaptive modulation techniques (e.g., digital video broadcasting—return channel system, or DVB-RCS).
The present invention includes techniques for mapping Ethernet packets for input into a series of frames having moving pictures experts group (MPEG) frames as output. This output of MPEG frames may ultimately be used as an input to a variable encoder and modulator processing block to perform adaptive modulation. With adaptive modulation, bandwidth is increased over conventional approaches of fixed encoding and modulation implementations. When applied to a communications system such as DOCSIS, variants of DOCSIS, or DVB-RCS communication systems, adaptive modulation facilitates installation of more subscriber modems on the cable system. More subscribers ultimately translates into additional revenue.
2. Related Art
DOCSIS is a series of specifications provided by CableLabs (www.cablelabs.com) to define a standard for cable modem headend and modem equipment. The cable modem headend (also known as the Cable Modem Termination System, or CMTS) provides a gateway between a wide area network from a central location to a plurality of cable modems (CM's) via a hybrid/fiber coaxial (HFC) interface cable. The DOCSIS specifications define the downstream as the direction of data flow from the CMTS to the CM's and the upstream as the direction of data flow from the CM's to the CMTS. DOCSIS specifies that the downstream data flow as a broadcast of MPEG frames which can be received by all CM's. These MPEG frames may contain DOCSIS frames. The DOCSIS frames may in turn contain DOCSIS management packets or Ethernet packets.
The Ethernet packets can contain either user datagram protocol (UDP) packets, Internet protocol (IP) type packets, or potentially other types of protocol packets. DOCSIS specifies the upstream as a time-division multiple access (TDMA) method of sharing upstream bandwidth to be shared among a plurality of CM's. The unit of time used in this TDMA implementation and CM sharing is called a mini-slot. The mini-slot is a programmable length of time fixed during initialization time of the CMTS. The bandwidth of the upstream is divided among a consecutive number of these minislots to be used either by one or more multiple CM's.
DOCSIS has also been adapted to work with communication systems other than the HFC interface between the CMTS and the CM. One of these systems is a fixed wireless system, whereby the gateway is called a Wireless Access Termination System (WATS) and the modem is called a Wireless Modem (WM). Another system that has adopted DOCSIS utilizes a two-way satellite system whereby the gateway is called the Satellite Modem Termination System (SMTS) and the modem is called the Satellite Modem (SM). The present application has primarily been adapted for the SMTS but is not limited to the SMTS and may be applied to other DOCSIS variants and non-DOCSIS variant systems.
One challenge in the conventional DOCSIS approaches, however, is that all MPEG frames are transmitted between the DOCSIS based SMTS and a corresponding SM system, based upon the same transmission parameters. The limitation that all of the MPEG frames must be transmitted using the same transmission parameters prevents the SMTS from efficiently utilizing and optimizing downstream bandwidth.
What is needed, therefore, is a process that enables a communication system such as a DOCSIS based SMTS to dynamically configure downstream MPEG frame parameters. This downstream configuring preferably occurs in a manner that efficiently allocates and optimizes available downstream bandwidth.